Drones flying over crowds are not normally a good mix—if there’s anywhere you don’t want four blades merrily spinning, it’s in the middle of a group of people. But nonetheless, Parisian police think they’ll be a useful tool for policing large gatherings.

The Paris police department has issued a public design brief, asking for companies to bring proposals for crowd-monitoring drones. The ideal design will have six rotors, a speed of 10 meters/second, a kilometer range, HD and thermal cameras, and a flight time of 30 minutes with a payload of 1kg. The cops are also looking for automatic and manual flight options.

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Those specs are right on the upper end of existing professional drones, but certainly feasible, for the right price. Using drones actually makes sense for police forces: helicopters have long been a tool for providing real-time aerial surveillance, but are orders of magnitude more expensive to operate.

With drones making that aerial surveillance much cheaper, the questions start being about overreach. Sure, drones are a proportionate and useful tool for policing large sports games, or riots. But it’s a slippery slope from there to targeting peaceful protests, activists, and basically anyone littering.